ABSTRACT The global water crisis demands efficient treatment of oily wastewater. While cationic polyacrylamide (CPAM) flocculation is widely used, conventional linear CPAMs face inherent limitations. These include molecular chain entanglement, which hinders pollutant interaction, and a rapid increase in solution viscosity with molecular weight, which reduces processability and efficiency. In response to these issues, research on branched CPAMs has been increasing. In this study, branched CPAM flocculants PADP1–6 and PADB1–6 were synthesized via aqueous free‐radical polymerization using 1,3‐propanediol (PDO) or 1,4‐butanediol (BDO) as branching agents. Optimal synthesis conditions were 0.28% PDO at 53°C with an acrylamide (AM) to methacryloyloxyethyltrimethylammonium chloride (DMC) molar ratio of 3.1 for PADP, and 0.23% BDO at 53°C with a ratio of 3.0 for PADB. The resulting polymers had intrinsic viscosities of 215.3 mL·g −1 (PADP) and 165.2 mL·g −1 (PADB), with PADP showing higher cationic degree. The optimal treatment conditions for the flocculants were a dosage of 80–90 mg·L −1 and a pH 7. Polymers with intrinsic viscosity ≥ 157 mL·g −1 and cationic degree ≥ 17% performed best. PADP3 achieved the highest removal rates (95.3 ± 0.53% oil, 93.2 ± 1.79% turbidity), outperforming its PADB counterpart. Both branched flocculants also surpassed the linear copolymer PAD and a commercial linear polyacrylamide in flocculation efficiency. Finally, Derjaguin–Landau–Verwey–Overbeek (DLVO) theoretical calculations indicated that the flocculation mechanism involved initial reduction of the interparticle energy barrier through charge neutralization, followed by enhanced aggregation via adsorption bridging. PADP exhibited stronger effects due to its higher cationic degree and molecular weight.
Bo et al. (2026) studied this question.